Process for obtaining aromatic hydrocarbons from oils and/or their residues rich in aromatic hydrocarbons and having a high content of unsaturated compounds

ABSTRACT

AROMATIC COMPOUNDS, E.G., NAPHTHALENE, PHENANTHRENE, ANTHRACENE, DURENE, ARE OBTAINED IN INCREASED YIELDS FROM OILS AND/OR RESIDUES RICH IN AROMATIC COMPOUNDS AND HAVING A HIGH CONTENT OF UNSATURATED COMPOUNDS, BY PRETREATING SAID OILS OR RESIDUES BY A THERMAL TREATMENT AT INCREASED TEMPERATURE IN THE RANGE OF 300-500*C. AND AT AN EXCESS PRESSURE OF 4-30 ATMOSPHERES, SUBJECTING THE PRETREATED MATERIAL TO FRACTIONAL DISTILLATION AND RECOVERING THE AROMATIC HYDROCARBONS FROM THEIR FRACTIONS BY COOLING AND CRYSTALLIZATION. THE AROMATIC COMPOUNDS ARE THEREBY RECOVERED IN INCREASED YIELDS AND INCREASED PURITY.

United States Patent Ofice 3,654,135 Patented Apr. 4, 1972 US. Cl. 208-71 6 Claims ABSTRACT OF THE DISCLOSURE Aromatic compounds, e.g., naphthalene, phenanthrene, anthracene, durene, are obtained in increased yields from oils and/or residues rich in aromatic compounds and having a high content of unsaturated compounds, by pretreating said oils or residues by a thermal treatment at increased temperature in the range of 300-500 C. and at an excess pressure of 4-30 atmospheres, subjecting the pretreated material to fractional distillation and recovering the aromatic hydrocarbons from their fractions by cooling and crystallization.

The aromatic compounds are thereby recovered in increased yields and increased purity.

I Numerous aromatic hydrocarbons of considerable economic' importance, for example, naphthalene, anthracene, durene and others are present not only in coal tar, which is the classic source for the recovery of these compounds, but also in other oils which are obtained in various large scale processes, e.g. of petrochemistry.

In their composition, these oils and residues differ from coal tar, among other respects, by their relatively high content of unsaturated, olefinic and aromatic-olefinic compounds. These unsaturated components make the recovery of aromatic compounds from said oils according to conventional methods rather difi'icult, or prevent it entirely, essentially for the following reasons:

(1) Said oils and residues rich in aromatic compounds contain said unsaturated compounds in addition to the compounds found in coal tar and they are, therefore, with respect to hydrocarbons, more complex mixtures than coal tar.

' (2) The unsaturated components have an excellent dissolving power for aromatic hydrocarbons, due to which the separation of crystalline material from the respective fractions is made difiicult and in some cases entirely prevented.

(3) In processing oils and residues rich in aromatic compounds, by distillation, the unsaturated compounds have a tendency to thermal conversions, by which a smooth distillation is rendered rather difficult.

For these reasons, the recovery of aromatic hydrocarbons by processing of said oils and residues has been considerably less productive and connected with considerably higher expenditure in comparison with processing of coal tar.

It has now been unexpectedly found that the disturbing effects of unsaturated components in processing of oils and residues, rich in aromatic compounds, can be extensively prevented, if the crude products or their fractions are subjected to a short treatment at increased temperature pressure. Under these conditions the unsaturated compo:

nents form polymers, the presence of whichin contrast to the presence of monomersdoes not adversely influonce processing. During distillation, said polymers remain in the sump product and can be easily separated from the hydrocarbons to be isolated. According to the present invention, the hot sump product is immediately drawn off from the distillation column, because the polymers formed would be in part depolymerized again under the existing conditions of temperature and pressure. Said depolymerization is preferably permitted to take place subsequently in a separate equipment.

The thermal polymerization of the unsaturated compounds present in oils and residues of varying origin can be carried out at temperatures between 300 and 500 C., preferably 350 to 400 C. and a pressure of 4 to 30 atmospheres. The reaction periods are relatively short. In most cases, the process is already completed after 10 to 60 minutes. Disturbing attendant phenomena, e.g., clogging of the apparatus by the polymeric ingredients formed, do not occur.

The effect of treatment by pressure and heat, with regard to the recovery of components from residues rich in aromatic compounds can be seen from the following examples. Thus, the yield of naphthalene from oil residues rich in aromatic compounds can be increased-4n comparison with the conventional processby an amount up to 92% Similar advantages can be attained in the recovery of other aromatic hydrocarbons, e.g., anthracene, phenanthrene and durene.

EXAMPLE 1 Percent Benzene homologs 0.5 Indene -h 1.0 Methylindene 5.7 Naphthalene 16. Dimethylindene 2.0

Naphthalene homologs, diphenyl and acenaphthene 20.0

Fluorene and homologs 5.3 Phenanthrene 2.0 Anthracene 0.8 Higher boiling compounds 7.9 Un-vaporizable components 38.4

After the thermal treatment the following distillation fractions are obtained:

I Percent Light oil a 4 Naphthalene oil 17 Alkylnaphthalene oil 21 Anthracene oil 1S Pitch 42' if the same residual oil, which is rich in aromatic compounds and has the above-described composition, is subjected, without thermal pro-treatment, to flash distillation, whereby the recovery of a normal pitch quality with a softening point (K.S.) of 67 C., at a column sump pressure of torr, an exit temperature of the tube furnace of only 280 to 290 C. is required, the following fractions are obtained by distillation:

The monomers polymerized by the thermal pre-treatment can be partially recovered from the pitch withdrawn from the distillation column, namely as unsaturated compounds, compounds saturated by addition of hydrogen or as compounds formed by cracking reactions. After the thermal treatment the pitch flows with a temperature of 300 to 320 C. through a waste pipe into a storage vessel provided with a vapor condenser. The polymers formed by the pressure and heat treatment and present in the pitch are here depolymerized at a pressure of 1 atmosphere and the secondary light oil distills off without additional sup ply of heat. The distillate is obtained in an amount of 1 to 2%, based on the crude residual oil and has the following composition:

Percent Methylindene l3 Methylindane 11 Indan 7 Dimethylindene 1 a-Methylstyrene 2 Styrene 1 Benzene homologs 32 Other compounds 33 The amount of secondary light oil can be increased if temperature and time of stay of the pitch are increased by further supply of heat.

EXAMPLE 2 The naphthalene oil obtained from an oil residue treated at 380 C., has a crystallization point of 71 C. and the following composition:

Percent Naphthalene 84 Methylindene 1 Dimethylindene Other compounds 15 By cooling to 20 C. and centrifuging 73% of technical naphthalene, having a solidifying point of 79.2 C. are recovered from this oil, corresponding to a yield of 74%, based on naphthalene present in the crude oil residue.

The naphthalene oil, obtained from said oil residue treated at 280-290 C. only has a crystallization point of 60 C. and the following composition:

Percent Naphthalene 70 Methylidene 8 Dimethylindene 3 Other compounds 19 By cooling to 20 C. and centrifuging, from this oil 54% of technical naphthalene having a solidification point of 789 C. are recovered, corresponding to a yield of 61%, based on the naphthalene present in the crude residual oil.

The increase of naphthalene yield by the thermal pretreatment from 61% to 74% corresponds to a yield improved by 21%.

' EXAMPLE 3 Crystallization of the anthracene oil from an oil residue treated at 380 C. starts at 30 C. By cooling to C. 2% of a crystallized product of the following composition is obtained:

Percent Phenanthrene 22 Anthracene 41 From said crystallized product phenanthrene and a n thracene can be isolated by conventional methods. For example, by two recrystallizations from the fourfold to fivefold amount of pyridine, anthracene is obtained in a yield of with a degree of purity of 98% (according to Montecatini). 13y redistillation of the mother liquor, the phenanthrene present therein is obtained with a degree of purity of (determined by gas-chromatography). The yield can be further increased by subjecting the anthracene oil once again to rectification, prior to crystallization.

In the anthracene oil obtained from the residual oil treated at 2'80-2'90 C. no separation of crystals occurs even upon cooling to 25 C.

The recovery of phenanthrene and anthracene by crystallization from the corresponding fraction has been rendered possible at all by the thermal pretreatment only.

EXAMPLE 4 500 parts of a naphthalene-containing oil which has been obtained from a residual oil rich in aromatic compounds as filtrate oil, are treated under superatmospheric pressure at 350 C. for 40 minutes. Prior to the thermal treatment, the oil has the following compositions:

Percent Naphthalene 32.7 Methylindenes 20.0 Other compounds 41.3

After the treatment under pressure and heat, the composition is as follows:

Percent Naphthalene 32.6

Methylindenes 3.7

Other compounds 63.7

From 500 parts of the untreated oil, by subsequent distillation under vacuum and thorough cooling of the naphthalene fraction to 20 C., 62.5 parts of technical naphthalene having a solidification point of 78.7 C. and a naphthalene content of 97.0% can be obtained, and this corresponds to a naphthalene yield of 37% based on the amount of naphthalene present in the charge.

From the oil subjected to the thermal treatment by analogous processing 105.0 parts technical naphthalene with a solidification point of 79.3 C. and a naphthalene content of 98.0% can be recovered, and this corresponds to a naphthalene yield of 63% based on the amount of oil charged in said treatment. Thus, conversion of the methyl-v indenes into higher boiling polymerized products brings about an increase of the naphthalene yield by 70% in comparison with the conventional process. If in the ther-- 300 parts by weight of a durene fraction of 30%, which contains mainly unsaturated compounds, preponderantly indene, is treated for 60 minutes at 400 C. under a pressure of 30 atmospheres. The oil, thermally pretreated in this manner, is distilled under normal atmospheric pres sure. From the fraction boiling between to 220 C., by centrifuging at ordinary room temperature, e.g., 18- 25 C., 49.5 parts by weight of durene having a melting point of 79 C. are obtained. This corresponds to a yield of 55%, based on the durene present in the material treated.

From 300 parts by weight of the oil not subjected'to the said pre-treatment under otherwise equal conditions, only 26 parts by weight of durene are obtained, corresponding to a yield 22 29%.

The recitation oil residue rich in aromatic compounds derived from pyrolysis of benzine to ethylene is used to denote an oil residue obtained by pyrolysis of crude benzine, at temperatures of 750-1000 C. to form ethylene, propylene and other gaseous hydrocarbons, pyrolysis benzine boiling up to about 180 C. and a residual oil boiling above 180 C. and rich in aromatic compounds. The abbreviation K.S. stands for Kraemer-Sarnow whose method for measuring the softening point is Well known in the art, see e.g. DIN 1995, February 1960, p. 18. The vacuum distillation can be carried out in the range of 50 to 760 torr. The parts and percent are by weight, it not otherwise stated.

The starting material, used in the above Examples 2-5, is a residue obtained in cracking and processing hydrocarbon oils rich in aromatic compounds, and having a high content of unsaturated olefinic and aromatic-olefinic compounds.

It will be appreciated that any hydrocarbon oil or its residue rich in aromatic compounds, and having a high content of unsaturated olefinic and/or aromatic-olefinic compounds can be used as starting material in carrying out the invention.

What is claimed is:

1. A process for obtaining aromatic hydrocarbons from a starting material selected from the group consisting of oils and residues of oils, rich in aromatic hydrocarbons and having a high content of unsaturated olefinic and aromatic-olefinic compounds, consisting in subjecting said starting material to a non-catalytic heat treatment at temperatures in the range of 300 to 500 C., under a pressure of 4 to 30 atmospheres during to 60 minutes in order to convert the unsaturated compounds into polymers; causing the material thus treated in direct sequence by release of the pressure to evaporate from said polymers and separating the polymers formed; distilling and con- 6 densing the rest of the material and recovering the aromatic hydrocarbons by cooling and crystallization from the condensed fractions.

2. A process as claimed in claim 1, in which the heat treatment is carried out in the range of 350 to 400 C.

3. A process as claimed in claim 1, in which products derived from pyrolysis of benzine are used as starting material.

4. A process as claimed in claim 2, in which products derived from pyrolysis of 'benzine are used as starting material.

5. A process as claimed in claim 1, in which a product derived from a cracking process is used as starting material.

6. A process as claimed in claim 2, in which a product derived from a cracking process is used as starting material. References Cited UNITED STATES PATENTS 1,441,341 1/1923 Govers 260-674 2,3 81,522 8/ 1945 Stewart 208-107 2,162,715 6/ 1939 Hancock 208-255 2,475,977 7/ 1949 Meier 260-674 N 2,775,629 12/1956 Anderson 260-674 N 2,910,426 10/ 1959 Gluesenkamp et al. 208-15 FOREIGN PATENTS 870,431 6/ 1961 Great Britain 208-15 HERBERT LEVINE, Primary Examiner U.S. Cl. X.R. 

